A Voltammetry Study of Ethanol Oxidation on Carbon Supported, Non Alloyed Platinum-Tungsten Catalysts

Abstract

The synthesis and characterization of bimetallic catalysts with Pt and W as active phases, supported on carbon, were carried out. A synthesis method based on the thermolysis of metal precursors was developed with systems in which an aqueous phase, an organic one and solid carbon are present. The Pt loading in the synthesized catalysts was kept constant and the amounts of W and carbon changed. It was found that the Pt phase forms hemispherical particles with average diameter of 3 nm. The W is predominantly in the form of hexagonal WO3 crystals with average dimensions 35 by 15 nm. No evidence of alloy formation is found. The electrochemical characterization of ethanol oxidation includes cyclic voltammetry and current–sampled voltammetry techniques. Tungsten exerts a promoting role in the activity of the catalysts, revealed by considerably increased current densities with respect to carbon–supported Pt. Details of this enhanced activity are revealed by cyclic voltammetry with different operating conditions and electrolyte formulations. These experiments allowed to identify the oxidation of adsorbed organic intermediates influenced by the tungsten phase. WO3 appears as well to cause the decrease in the rate at which Pt oxides reduce, leading to higher surface coverage of OH• species.